Press TV, Iran’s English-language channel, aired a documentary on the city of Natanz, focusing on the nearby uranium enrichment facilities. The December 11 documentary showed the cascades of centrifuges and other installations within the facilities, while explaining the workings of the nuclear fuel cycle.
Narrator: "After a short trip around the city of Natanz, I decided to go to the Natanz uranium enrichment center and visit the remaining tourist attractions around the city at another time. This is the road that overlooks the Natanz uranium enrichment facility. The knowledge to produce and make use of nuclear fuel is one of the most complicated and advanced new technologies in the world, which has evolved in this part of our country. The Natanz uranium enrichment facility is currently the sole uranium enrichment facility in Iran, which is operating on the outskirts of the city of Natanz. This center and its rotating centrifuges are moving the nuclear fuel cycle forward, while managing to place us among countries that possess uranium enrichment technology. After the valuable substance of uranium hexafluoride, or enriched UF6, that contains 0.7% of the U-235 isotope, is produced at Isfahan's UCF [uranium conversion facility] factory. It's transferred to this place in special standard cylinders under a series of safety principles and under the supervision of the safeguard department of the Atomic Energy Organization of Iran for enrichment under 3.67 percent.
"The Natanz uranium enrichment facility contains various departments and buildings in which primary and secondary processes of uranium enrichment are carried out. The primary process in uranium enrichment consists of supplying at the feeding station the enrichment process in the centrifuge hall and the collection of the final product in the collection unit. Special cylinders containing solid uranium hexafluoride gas, or UF6, turn into gas after passing through this autoclave machine. After the weight of this gas is precisely measured, it is transferred to the centrifuge hall for enrichment.
"In this hall, which is known as the feeding hall, standard 48x cylinders from the UCF center in Isfahan are transferred into the autoclaves in special wagons on a rail track, as they are very heavy. Solid UF6 is heated in these autoclaves in proportion to the consumption of the centrifuge cascades so it would exit the cylinders as gas and move toward the centrifuge hall through special pipes."
Scientist: "The process at the feeding unit in which we are now standing in is as follows. The UF6 transferred from Isfahan enters this unit and after entering the cylinder and being weighed it enters the autoclave where it's heated and the solid UF6 inside the cylinder turns into gas and is transferred and injected into the centrifuge hall. The condition of the autoclave is controlled through an instrumentation system, which includes barometers and thermometers to ensure a uniformed supply chain is injected into the cascade hall. This process is necessarily carried out by experts and through controlling the precise weight of the injected gas to the cascade hall that accommodates the centrifuges."
Narrator: "Uranium enrichment is one of the most important nuclear fuel cycles. There are three naturally occurring isotopes of uranium in nature, which are Uranium-234, Uranium-235, and Uranium-238, among which Isotope 235 easily splits under special conditions and frees a lot of energy but since the natural uranium it contains is only a small amount, about 0.71 grams, in order to produce energy, it should go through the enrichment process to reach three or four percent. The process of increasing the percentage of the 235 isotope is called enrichment.
"When uranium hexafluoride particles, or UF6, is placed inside the centrifuge machine and subjected to the centrifugal force, Uranium-238, which is heavier than Uranium-235, is separated and accumulates on the walls of the centrifuge machine. The separation unit, which is the most important phase of the enrichment process, increases the mass of Uranium-235 isotope from 0.7 percent to 3.67 percent. This cascade accommodates many centrifuge machines. Each cascade contains 164 or 174 centrifuges that are designed in parallel. Each cascade is composed of 15 or 17 levels.
"Whenever we come into this hall, I notice this sound that we can hear which is very disturbing. Where is it coming from?"
Scientist: "This sound is produced by the centrifuge machines that are working and completing the enrichment process. As we said before, UF6 gas is transferred to the cascade hall through these pipes from the feeding unit. In the cascade hall, the centrifuges complete the enrichment process through imposing centrifugal force on the UF6 particles and UF6 gas is separated after heating, which makes it lighter inside the machine. Since this separation process is done in phases and step by step, it produces an image like a cascade and this is where the word cascade is derived from for the enrichment chain. After the UF6 is enriched from 0.7 percent to 3.67 percent, the enriched product exits the initial stage of the chain and is transferred to the feeding and collecting units to be placed in standard cubic cylinders, which are used for enriched products before being transferred to Isfahan."
Narrator: "Centrifuge machines have different types or, as said, belong to different generations, like IR1, IR2, IR4, and IR6, among which the IR6 is one of the newest and most advanced centrifuge machines, which is capable of enrichment that's 10 times more than the IR1 machine. The advanced IR8 centrifuge machine, which is currently being tested, is 24 times more powerful and has enrichment capacity that's 20 times higher than the present machines.
"Hexafluoride gas, or UF6, is injected into the rotation center of the centrifuge machines, and then, by moving in two directions along the axis and walls, it causes isotope concentration along the axis. As a result of this process, light and heavy isotopes are collected from the two ends of the axis near the centrifuge wall. Centrifuge machines are made of some 100 parts. These parts have been put together and prepared for use with the consultation and help of a group of experts and scientists in various industrial fields. These machines are so sensitive, even sweaty hands during the assembling process can deliver a sledgehammer effect on the machine when it's spinning 500 times per second and cause it to fail."
Scientist: "UF6 gas enters the cycle through the pipes I told you about, which are called antennas and after separation it returns through the same antennas."
Narrator: "You mean it returns from up there?"
Scientist: "In the pipes... yes. The instrumental control equipment that is placed on the enrichment chain under the solenoid valves, the air solenoid valves located under the barometers and thermometers are controlled by operators so they would be able to control the amount of gas injected into the machines and eventually control the amount and enrichment of the product it aims to receive from the chain."
Narrator: "After injecting the UF6 gas into the machines, isotope Uranium-235 and 238 are separated through centrifugal force that is caused by the high-speed spinning of the rotor that reaches 1,000 rounds per second, and the enriched gas is transferred to the machines in the next phase through the gas supply system. The gas that no longer contains isotope 235 is returned to the previous phase of the chain so that enrichment is completed. During the enrichment process at this complex, the enrichment of the product is controlled by measuring instruments and pressure regulators. Also, after injecting food to a chain of machines, a sample is taken from the output current and analyzed with special machinery so that the enrichment at the centrifuge cascades can be determined. After my visit to the centrifuge hall, I once again went to Natanz to visit other places around the city.
"After meeting with the youngest museum owner in our country, Iran, I once again headed back to the Natanz enrichment facility to observe the next phases of uranium enrichment. Uranium hexafluoride gas, or UF6 is collected in CV cylinders after exiting the centrifuge machine."
Scientist: "This unit is where the products manufactured in the centrifuge hall are collected. The products manufactured in the cascade enter this unit after being transferred through connecting pipes. They are then refrigerated using UF6 physical properties and become condensed in these boxes at minus 25 degrees centigrade, with the increasing pressure produced by the pumps and are collected in cylinders so they would be ready to be transferred to Isfahan."
Narrator: "In the third unit of the Natanz uranium enrichment facility, the UF6 that is enriched and depleted by cold traps, which is responsible for cooling and freezing the UF6 gas, is collected and separately accumulated in CV cylinders. The CV cylinders, that weigh over two tons, are filled in layers by the centrifuge machines, and differ in the percentage of enrichment. In order to homogenize the mixture, enriched UF6, or uranium hexafluoride is placed in an autoclave machine under certain conditions so it turns into liquid."
Scientist: "As I told you before, the product that is accumulated in the CV cylinders is in layers, which differ in the percentage of enrichment. Since we need to have a homogenized mixture inside the cylinders, the cylinders are placed in an autoclave under certain temperature and pressure conditions so that the solid substance inside the cylinder turns into liquid and becomes homogenous. After it becomes homogenous, samples are taken and the percentage of enrichment is determined, then the cylinder is transferred to Isfahan for producing fuel rods."
Narrator: "Yes, yes... Thank you.
"The entire storage process is observed by experts in this control room. Since the feeding of the centrifuge machine begins, they are stored in CV cylinders, and transferred to Isfahan's uranium conversion facility (UCF). The censors placed on the centrifuge machines inform the experts of any minor changes. The experts in this room control the pressure and analyze the production in each cascade, and are well aware of the amount of production and the percentage of enrichment in each centrifuge hall. After ending my visit to the Natanz uranium enrichment facility, I went to the grave of a martyr, laid to rest at this facility, to pay tribute to all those who lost their lives, defending our beloved country.
"Without a doubt, the precious achievement of producing and assembling centrifuge machines, and achieving enrichment knowledge on an industrial scale, has only been achievable by relying on the willingness and capability of our youths, and is considered a major accomplishment for our country in the region. Goodbye for now, and until our next story."